Numerous types of suspension systems and arrangements have been divised to provide a smoother ride for vehicles including vehicles having non-driven axles of the type mounted on trailers, trucks, recreational vehicles and the like. Suspension systems also have been devised for use with vehicles having such non-driven axles which include a pair of separate axles on each side of the vehicle with a single wheel or pair of wheels being rotatably mounted on the stub shaft of each axle. These axle pairs have been interconnected by various suspension systems in an attempt to equalize load exerted on the individual tires.
Heretofore, these axle pairs and associated wheels were interconnected by suspension systems utilizing a trailing arm and leading arm arrangement separately or together with a walking beam. These types of suspensions result in an unbalanced force being exerted on the forward tire which causes that tire to dig into the roadway and causes the rear tire to lift from the pavement during braking. This trailing-leading arm suspension arrangement causes a "chatter" effect on the rear tires during braking resulting in chatter tire tread marks on the pavement and excess vibration on the trailer frame and cab. Also, the excessive force applied to the leading arm of the suspension system can seriously damage the arm and axle.
These prior suspension systems also have incorporated into the leading and trailing arm arrangements and connecting walking beams an intervening steel coil or leaf spring or elastomer spring member to increase the smoothness of the ride. Examples of these prior suspension systems are shown in U.S. Pat. Nos. 2,361,496; 2,410,747; 2,493,024; 2,742,301; 2,743,939; 3,410,573; 3,528,680; and 3,539,198.
Some of these problems have been eliminated by providing the suspension system with a dual trailing arm arrangement in which both of the wheels are rotatably mounted on the end of trailing arms which are pivotally mounted on the vehicle frame forward of the wheels. Also, the wheel mounting arms are interconnected through levers and an intervening rubber spring located between the extended ends of the levers to provide for a smoother ride. U.S. Pat. Nos. 3,749,417 and 3,768,827 are examples of such suspension systems and are believed to be the closest prior art to the suspension system of our invention.
Although the dual trailing arm suspension systems of the type shown in these two patents do overcome some of the difficulties with the prior trailing and leading arm type of suspension systems, they are limited in certain aspects. The length of the levers which are connected to the trailing arm pivot assemblies and are engaged with the elastomer spring must be equal to at least one-half the distance between the wheel axles. This requirement seriously limits the versatility that can be obtained by the suspension system since the ratio between the lengths of the levers and trailing arms and the included angle therebetween cannot be easily adjusted. This prevents obtaining various suspension characteristics, which can be achieved by varying these parameters, for matching the suspension system to the desired ride characteristics and load carrying capability of the vehicle on which the suspension system will be mounted. Also, the axial length of the rubber spring placed between the overlapping lever ends is limited since this length must be maintained relatively short to avoid interference with the vehicle frame at one end and low ground clearance at the other end.
Although some of these prior suspension systems do perform satisfactorly in many situations, they do not provide the desired versatility and balanced force distribution during braking and upon contacting road obstructions. Accordingly, the need has existed for an improved suspension system which uses a pair of trailing arms in combination with an elastomer spring to provide a smooth ride and to distribute the braking forces and road vibrations equally onto both tires that support the trailer or the vehicle body.